The invention relates to an apparatus and method for emitting light. The invention also relates more particularly to a silicon-based light-emitting diode for emitting light that may include wavelengths in the ultraviolet portion of the electromagnetic spectrum.
Light emitting diodes, or LEDs, are known per se. Conventional LEDs utilize the semiconducting properties of materials such as silicon.
In a conventional LED, light is generated when free electrons drop from the conduction band of a semiconducting diode into energy holes. Each such event releases energy in the form of a photon, with the wavelength of the photon depending upon the energy gap between the conduction band and the holes. As the energy gap becomes larger, the photons released likewise become more energetic. The more energy an individual photon has, the shorter its wavelength.
The principles governing the operation of conventional LEDs are well known, and are not further described herein.
However, known LEDs suffer from several limitations.
For example, the wavelengths that may be produced are limited by the magnitude of the energy gap. The shorter the wavelength of light that is to be emitted, the larger the energy gap must be. It is therefore particularly difficult to produce light with short wavelengths, in particular ultraviolet light, using known LEDs. In principle, it is possible to produce a semiconducting LED with an energy gap large enough that it emits ultraviolet light, i.e. light having a wavelength of less than about 400 nm. However, such LEDs are difficult to produce, expensive, and inefficient.
Indeed, silicon-based LEDs are extremely inefficient emitters of light in general. The best reported efficiency for a silicon-based LED of conventional design is 0.8%. That is, no more than 0.8% of the energy applied to that LED is emitted as light, the remainder typically being lost as heat.